Circuit breakers are employed to interrupt AC or DC, single-phase or multi-phase electrical circuits when electrical fault conditions exist. The electrical fault conditions can include an instantaneous current in the electrical circuit that exceeds a predefined instantaneous current limit (i.e., an electrical short exists) or a long-term current that exceeds a predefined long-term current limit (i.e., an electrical overload exists). A single-break MCCB typically comprises one stationary contact mounted to a stationary current loop and a movable contact mounted to a rotatable contact arm for each phase. A dual-break MCCB comprises two stationary contacts and two movable contacts for each phase. In normal operation when electrical current flows through the device the movable contacts are in contact with the stationary contacts and the breaker is in the closed state. In the presence of an electrical fault the flow of electrical current is interrupted by separating the movable contacts from the stationary contacts, and the breaker is going from a closed to a tripped state. The contact arm is moved from a closed to a tripped position by means of a mechanism that acts on the contact arm.
The energy to move the contact arm may also come from electromagnetic fields that develop around the stationary current loop and the contact arm due to the electrical fault currents that flow through these components. The interactions between the electromagnetic fields and the fault current result in a repulsion force between the stationary current loop and the contact arm which, in conventional approaches, causes the contact arm to rotate and separate the movable contact from the stationary contact. As the movable contact begins to separate an arc may form between the stationary contact and the movable contact. Due to the electromagnetic fields there will be an arc force acting on the arc and affecting its path. The magnitudes of the repulsion force and the arc force diminish as the fault current and electromagnetic field intensity drop and as the alignment of the rotating contact arm with respect to the stationary current loop and with respect to the electromagnetic field becomes less favorable as the contact arm rotates.
The movement of the contact arm from the closed to the tripped position has to be fast to limit current and to minimize formation of arcs that may degrade the contacts. The circuit breaker mechanism also has to be of suitable size to fit in a predefined circuit breaker casing or electrical panel. Therefore, there is a need for maximizing the repulsion forces that accelerates the contact arm and for reducing the size of the mechanism.